Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.53   9.611%   $102.5192   $102.52   $102.50   $102.50  
  Purchase #2 $16.28   4.578%   $17.0253   $17.03   $17.05   $17.00  
  Purchase #3 $60.87   7.492%   $65.4304   $65.43   $65.45   $65.40  
  Purchase #4 $167.64   4.259%   $174.7798   $174.78   $174.80   $174.80  
  Purchase #5 $213.37   9.228%   $233.0598   $233.06   $233.05   $233.10  
  Purchase #6 $216.46   6.636%   $230.8243   $230.82   $230.80   $230.80  
  Purchase #7 $34.31   9.143%   $37.447   $37.45   $37.45   $37.40  
  7 purchase totals = $802.46       $861.0858   $861.09   $861.10   $861.00